Testing apparatus for determining the operate and release currents of relays



J. w. .MCGRATH 3,250,988

OPERATE v I May 10, 1966 TESTlNG APPARATUS FOR DETERMINING THE AND RELEASE CURRENTS OF RELAYS Filed Dec. 6. 1960 Jzum gqaru T TURN-E1 and the :release current of'the coil under test.

meter may be .considered to be a meter which measures a current increment'which in the present case would .be

3,250,988 Patented Ma i 9 'TIESTING APPARATUS FOR DETERMINING THEwOPERATE AND RELEASE CURRENTS F RELAYS John W. McGrath, Allentown, Pa., assignor to Western glecltfic Company, Incorporated, va corporation of New or Filed use. 6, 1960, s... No. 74,060 1 Claim. c1. s24 2s This invention relates to relay testing and more parttcularlyto a relay testing circuit which indicates the I difierence between the operate and release currents of a relay.

In the testing of relay switches, it is important to as-.

certain the just operate" current and the difference between that current and-the just release current so that the circuits in which they are eventually to be used. It .hasbeen the prior practice to obtain the operate and release current readings by separate testing operations and to then subtract the release current reading from the operating current reading to obtain theditference.

It is an object of the present invention to provide a relay switchtesting circuit which automatically indicates the difference between the operating and release'currents.

eluded whether the switches-are individually tested or" whether complete relays aretested. l

The invention will now bedescribedid-greater detail by reference to thedrawing, wherein: r I FIG. 1 is a schematic circuit. illustration of the invention; and e f FIG. 2. is a control circuit forzcontrollingjthe operation of the test circuit.

In the drawing, two tubesfll-and IZ-are shown connected in inverse relationshipto provide currents i and i,. The. input of tube 11 includes.acresistor-capacitor network provided by 'the components R and C while similarvly, the .inputoftube lzincludesa resistor-capacitor nettherelay switches meet the operating requirements of It is a further object of the present invention to provide in a relay switchtesting circuit, an indication of the operactingcurrent, together with an indication of the difference between the operating and release currents;

Other object's'and advantages of the invention will be- .come apparent from the remaining desciption.

In carrying out the invention, there is provided a switch testing apparatus comprising a first circuit adapted to v produce an operate current flow through a coil which operates a switch, andxa second circuit connectible across the. coil and adapted to produce a current flow which reduces the operate current flow. In making a test, the first circuit is enabled and when the current therein reaches the operating value, the switch under test is actuated and the just operate current is stored. Actuation of the'switch conditions the second. circuit for current flow, and the latter current acts to diminish the operate current until the current flow through the coil is such that the switch'is released. A meter in the second circuit indicates the amount of current flowing therein when the switch is released. This reading, therefore, represents the difference between the operate and release currents of the switch under test.

In one embodiment the invention utilizes a vacuum tubecircuit'for measuring the difference between operate and release currents for switches actuated by a coil connectible in the plate circuits of two tubes connected in inverse relationship. A meter in the plate circuit of the first tube is utilized for measuring the just operate current and a deltameter in the plate circuit of the second tube measures the difference between the operate current A delta a current representative of the difference between the relay-operate andrelease currents. Each of the tube 'mput circuits is provided with a resistor-capacitor network for bringing the plate current up to the proper value and holdingiit for reference.

While the invention is described inconne'ction .with a relay coil into which switches, suchas mercury switches, .to be tested areinserted, it is to be understood that, ac-

cording to the present invention, various other switches may be'tested or a separate complete relayincluding a switch .or switches may be tested during each testing I operation. Suitable plug-in arrangements may be inwork provided by the component R, and 0;. Further,

the inputof'tube 11.:inc1udes ash/itch 14 which is closed at the start-of a testing operation, and the input of tube 12 includes a switch16-which :is normally open at the start of a testingoperation.

In practicing the invention, a switch to be tested such as a mercury switch 15,-1is inserted into'the coil 13 shown between terminals 18 and'19' and maintained therein .in any .convenient manner. (Switch 14 is then operated to its closed position, causing current to'flow in the plate circuitof tube .11 as thevoltage applied to the capacitor .C builds up, that is, the voltage becomes less negative.

Whenthe currentthrough the coil 13-rises to the operate point, :the switch 15 un'clerltest isactuated and, through an appropriate relay circuit shown .in "FIG. 2, switch 14- isopened, leavingthe capacitor C with a fixed input biasing volt-age. 0n opening of switch 14, switch 16 is closed to enable conduction intube 12, the input'biasing voltage for'which is built upr-in accordance-with the current characteristics of'the R -C network. As'the current of plate circuit in the tube 12: increases, "the current through the coil 13 diminishes, a point-being reachedatswhich the-relay defined by coil 13 and'switch 15 is released and thereby opens'the cwitch 16. "At'therele'ase time a'steady grid bias voltage is applied to tube 12 from the capacitor C 'sim'ilar to the steady. 'grid bias applied to the tube 11 by'the capacitor C. '.Delta.:meter'22now gives an indication ofthe amount of which has been substracted from the operate current and which was required to release, 7

the relay. The charge on capacitor C and C may be reduced to cutoff in any convenient manner, if necessary. Thus, tubes Hand 12 respectively m'ay beplaced'in a cut-off condition by means-of suitable discharge. circuits 32 and33. v.

FIG. 2 showsa simple control 'circuitfor controlling the operation of the testing circuit shown in FIG. 1. Initially, both tubes 11 and 12 are biased :to cutoff so that, no plate current-flows inv either. Closing control switch 30 operates relayt-20 which, by actuation of switch 14 completes thecircuit from-"thergrid of tube .11 to a source of voltage less :negative' *thanrthe cutoff voltage.

Current inrthe-output'of tubeilbuilds up until the switch under test l5-operates, andrtran'sfers from the L tojthe R position, which,'in turn releasesrelay 20 and opens switch 14, preventing further current increase. Capacitor C maintains the. grid voltage and'plate current for further.

reference. Control switch 31'rnay :'now'be closed to operate relay '25-,thereby actuating switch 16 and closing the input circuitoitube .12. Current builds up, in the output oftube llyas'describedin .connectionwith tube 11 until the switch under test is released andtransfers from the R positionzto the L-positiou; The two curreritswhich are of 'interestmay nowberead :from the meters. 21 and 22. 6

Various departures emay be gmade from the invention as described without -depattu.reifrom*'thexspirit or scope of theinvention. Y I 1 What is claimed is: A relay switch-testing apparatus comprising vacuum tube and a second vacuum tube, the plate of the first vacuum tube being coupled over a first circuit path to the cathode of the second vacuum tube and the plate of the second vacuum tube being coupled over a second circuit path to the cathode of the first vacuum tube, a

relay including a coil and a switch to be tested, the relay coil having one terminal connected to a point in the first path and the other terminal connected to a point in the second path,,,a first'meter connected in the first path between the plate of the first vacuum tube and the point to which the one terminal of the relay coil is connected, -a second meter connected in the second path between the plate of the second vacuum tube and the point to which the other terminal of the relay coil is connected, a biasing input cirucit for the first vacuum tube including a biasing source, a resistor, a capacitor coupled to the input grid of the first vacuum tube, and a first switch, closure of the first switch connecting the resistor and capacitor in series across the biasing source for initiating conduction in thefirst vacuum tube to provide a current of increasing magnitude for operation of the relay switch under test, a biasing input circuit for the second vacuum tube including a biasing source, a

4 resistor, a capacitor coupled to the input grid of the second vacuum tube, and a second switch, and control means responsive to the actuation of the relay switch when the current through the relay coil reaches the operate value for opening said first switch and closing said second switch to connect the last mentioned resistor and capacitor in series across the last mentioned biasing source for initiating conduction in the second vacuum tube to provide a currentwhich increases in magnitude until the relay is released, the control means being furtherresponsive-to the release of the relay switch when the current through the relay coil diminishes to the release value for opening said second switch.

References Cited by the Examiner UNITED STATES PATENTS 2,229,806 1/ 1941 Holzler 328-81 2,432,092 12/1947 Ferrell 32428 WALTER L. CARLSON, Primary Examiner. SAMUEL. BERNSTEIN, Examiner. G. L. LETI, Assistant Examiner. 

